Re: AAT Theory
David L Burkhead (r3dlb1@dax.cc.uakron.edu)
27 Sep 1995 11:26:11 GMT
In article <hubey.812095867@pegasus.montclair.edu> hubey@pegasus.montclair.edu (H. M. Hubey) writes:
>r3dlb1@dax.cc.uakron.edu (David L Burkhead ) writes:
>
[ 8< ]
>
>We have exactly the same problem with the savannah theory
>assuming that it still exists :-)..
Which "savannah theory" are you talking about? The one that
involves a more mosaic environment or the treeless, waterless
strawman?
>
>Today's humans have long legs and can run reasonably fast but
>it seems they would have been faster on all fours. Besides, if the
>knee joint had to go through the change from the quadripeds to
>the humans, somewhere in the middle when the twisting and turning
>was supposed to be happening (I guess at the hips too) the animal
>would have practically been lame. Where could it have survived?
A) Nobody ever said that humans were adapted to running speed.
Thus, comparing comparing it to claims of "streamlining" is a
non-sequitor.
B) All "higher" primates, particularly the great apes, adopt
varying degrees of bipedal locomotion. Chimps and gorillas sometimes
walk bipedally. Gibbons _always_ do so on the ground. I don't know
about oranguatans, but they do walk bipedally at least sometimes,
maybe most or all of the time when on the ground. Since primates
already have the ability to walk bipedally, it is not surprising that
one branch specialized in that form of locomotion. They _may_ have
traded running speed on the ground for other advantages (several of
which have been detailed here), but even that's not as certain as some
would think. I don't recall that chimps or gorillas, more quadrupedal
primates, are particularly fast runners either.
C) That _you_ cannot envision a series of gradual improvements in
bipedal locomotion, in an animal that already _had_ the capability to
use it at least some of the time, does not mean that I am so limited.
Arguments from ignorance are rarely convincing. That's why they are a
logical fallacy.
>The theorizing in this field is like thermodynamics-- they
>concentrate on states not the dynamic paths. If it were not
>so how does anyone explain how some animals suddenly(!)
>stopped laying eggs and decided to carry their babies inside
>them.
You betray your limited knowledge here. (Well, my knowledge is
limited too, as is anybody's, but, in this subject, it appears to be a
bit less limited.) There is no "suddenly" involved. We have animals
that lay eggs and leave them. We have animals that lay eggs and stay
to protect them. We have animals that lay eggs and _carry_ them with
them. We have animals that allow a bit more development _within_ the
mother than just fertilized eggs. We see animals whose eggs have
thinner shells than others. We see animals where they dispense with
the shell entirely and carry the embryo externally (albeit in a
"pouch" in the cases I can think of offhand).
No. There's no "suddenly" about it.
>
>We see that they exist and try to go backwards even if
>unsuccessful. We have streamlined humans without body
>hair and with things like the diving reflex. The rest
>is story making like all the rest.
Again with the streamlined. That's a _claim_, not a "fact."
Furthermore, it's a claim that does _not_ fit the conclusion of a
"wading ape." In fact, a hairy body would have _less_ drag for that
upright wading ape. Go look up turbulent vs laminar flow separation
drag in bluff bodies. (This kind of thing is one of the reasons the
"obvious" is so often wrong.)
>> So, were our ancestors, who were the direct decendents of those
>>aquatic apes, "streamlined"? It would not appear so.
>
>It doesn't matter much to me. I'm convinced given the evidence
>that the aquatic phase seems to hold promise. Maybe the aquatic
>phase goes back even further and the apes of today came out of
>the water and went into the trees and humanoid ancestors spent
>more time in the water.
That you are convinced by evidence that is often either
irrelevant or just plain wrong says more about your credulousness than
about the viability of the theory.
>
>> Sigh. Go back and read what I said. Traits that we developed
>>_after_, long after, any purported aquatic lifestyle was _over_ cannot
>>be used as evidence for that lifestyle. Your citing grasping thumb
>>and fingers is a total non-sequitor. If we developed those traits in
>>an arboreal lifestyle then we had them then. It did not take several
>>million years _after_ we climbed down from the trees before those
>>hands showed up. _All_ of our ancestor species, right back to the
>>earliest known hominids, had them.
>
>I'm still not clear why it can't be so. Streamlining was a small
>part of what I wrote about. If the changes had taken place in
>response to water, then if the change was useful it would have
>stayed, just like being able to grasp didn't go away when our
>ancestors came out of the trees because it was useful.
What's to not be clear about? If we somehow "lost" the
streamlining as australopithecines, then regained it again as homo
sapiens, we must have gained it for other reasons. If we gained it
for those other reasons, then they are sufficient in themselves to
explain it without invoking any aquatic phase. You just cannot cite
traits that clearly did _not_ develop in an aquatic phase as evidence
for an aquatic phase and retain any credibility whatsoever.
>
>Besides, as I wrote in another posting, maybe the whole
>hand and foot changes in proto-humanoids did develop in water.
>For example long digits would make webbing useful but certainly
>not something like a dog's paws. A wide foot with webbing would
>make swimming easier. And it didn't have to mean that the hair
>was lost by that time, since neither polar bears nor sea otters
>have lost their hair. Some of the could have gone onto the
>trees and others stayed in the water longer.
Why invoke an aquatic phase for long digits since _all_ the apes,
and every monkey species I know already has them? Once again, you
cannot invoke an aquatic phase to "explain" traits that developed
elsewhere and retain any credibility whatsoever. Furthermore, the
chimp/ape foot, with its long toes and separated first digit is a much
better canditate for aquatic propulsion than the hominid/human foot.
This would then seem to contradict your hypothesis.
>>lifestyle, then the trait would have to have developed _while we were
>>still in the water_. Since A. Afarensis does not have such
>>streamlining, the aquatic phase would have had to have been _after_
>
>Everything is relative. If it doesn't look just like a monkey
>and is even slightly more bipedal it is more "streamlined" and
>we don't know if it had webbing to make up for its lack of more
>streamlining and I guess we don't know if it had hair either.
Once again, you are making assumptions about "streamlining" that
are just plain not justified. And the more assumptions you keep
piling on the case, the less tenable it becomes.
>
>>i.e. that humans have a lower Cd when swimming or wading (mostly
>>wading since that's what the theory is based on) than would chimps or
>>gorillas, or whatever ape most closely approximates the common ancestor.
>
>Wading, swimming, diving, dunking, what is the big deal?
Adaptations for wading are not adaptations for swimming are not
adaptations for diving are not adaptations for ducking. And the Cd of
the body posture for one activity will _not_ be the same as the Cd for
another. Aren't _you_ the one suggesting taking a few fluid mechanics
courses? Why not take your own advice?
>
>Wading is just a word; I assume it was meant to explain how
>they got started.
You assume wrong. Wading is more than "just a word." It is the
label attached to an _activity_. Wading and swimming are _not_ the
same things. It's not clear that humans are "more streamlined" than
apes or monkeys for swimming, and it is _certainly_ not clear that
they are more streamlined for wading (and "streamlining" for one is
not the same as "streamlining" for the other).
Also, wading is not just how the so-called aquatic ape "got
started." It's supposed to have been their primary activity for a
million+ years. It's supposed to be a critical factor in why we are
bipedal, and you just can't get that from swimming--the adaptations
are all wrong. Of course, they're all wrong for wading too, but
that's another story.
David L. Burkhead
r3dlb1@dax.cc.uakron.edu
d.l.burk@ix.netcom.com
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